Tip/tilt Alignment for a Fizeau Interferometer via Defocus-Based Sub-Spot Separation

It is a crucial premise for Fizeau interferometric imaging that all the optical axes of sub-apertures are well aligned. What is challenging in tip/tilt alignment of such interferometers is the superposition of all the sub-aperture spots on the focal plane for generation of fringes. In this paper, we propose and demonstrate a simple tip/tilt alignment scheme via defocus-based sub-spot separation (TADS). The focal interference function is divided into sparse defocused sub-spots at a long defocusing distance. Then the servo-control technology with a centroid extracting algorithm is used to align all the sub-aperture optical axes, each corresponding to a defocused sub-spot. The pointing correction performance using TADS has been verified through closed-loop experiments performed on a Fizeau telescope array testbed newly built in our laboratory. Compared with the current means, the proposed TADS eliminates the requirement of complex hardware design and the limitation of sub-aperture amounts, which is compatible with most existing segmented mirrors and telescope arrays.